Battery cushioning material

Abstract

This battery cushioning material (10) comprises a plurality of displacement absorbers (11) disposed between a plurality of battery cells (2). The displacement absorbers (11) each comprise: cell contact surfaces (12A, 12B) that contact the battery cells (2); and a displacement-absorbing portion (13) that protrudes in a first direction away from the cell contact surfaces (12A, 12B) and has a cross-sectional area that decreases proceeding away from the cell contact surfaces (12A, 12B). Adjacent displacement absorbers (11) are continuous at end portions (121A, 121B) that serve as the starting points of the change in area on the cell contact surface (12A, 12B) side.

Description

Battery buffer material

[0001] The present invention relates to a battery buffer material.

[0002] In a secondary battery, a configuration in which a buffer material is disposed between a plurality of battery cells is known (see, for example, Patent Document 1). The battery of Patent Document 1 disposes a heat insulation buffer material between battery cells to absorb the gap variation between cells by elastic deformation. This heat insulation buffer material is composed of an elastic block having a cross-sectional shape sandwiched between opposing battery cells and a flat connecting film connecting adjacent elastic blocks.

[0003] Japanese Patent Application Laid-Open No. 2023-66771

[0004] However, in the battery buffer material of Patent Document 1, since a flat connecting film is disposed between the elastic blocks, the surface pressure escapes at the portion of the connecting film, and the surface pressure acting on the battery cells becomes non-uniform. In particular, in a all-solid-state battery, compared with a battery using a liquid for the electrolyte, the displacement difference (stroke length) during expansion and contraction during charge and discharge becomes larger. If there is variation in the surface pressure applied to the battery cells, the contact area between the solid electrolyte and the cathode active material in the battery cells becomes smaller and the battery performance deteriorates.

[0005] An object of the present invention is to provide a battery buffer material capable of applying a uniform surface pressure to battery cells.

[0006] In the battery buffer material of the present invention, a plurality of displacement absorbers are disposed between a plurality of battery cells. Each of these displacement absorbers includes a cell contact surface that contacts the battery cell, and a displacement absorption portion that protrudes in a first direction away from the cell contact surface and has a cross-sectional area that decreases as it moves away from the cell contact surface. Adjacent displacement absorbers are continuously adjacent to each other at the starting point of area change on the cell contact surface side. Therefore, since the displacement absorption portions are disposed without gaps between the battery cells, there is no escape of surface pressure, and a uniform surface pressure can be applied to the battery cells.

[0007] Fig. 1 is a schematic cross-sectional view showing a secondary battery according to an embodiment of the present invention; Fig. 2 is an enlarged cross-sectional view showing a portion of a battery cell according to the embodiment; Fig. 3 is a cross-sectional view showing the configuration of battery cushioning materials arranged between battery cells according to the embodiment; Fig. 4 is a schematic view showing the arrangement position of battery cushioning materials according to the embodiment in the XY plane; Fig. 5 is a cross-sectional view showing the configuration of battery cushioning materials arranged between battery cells according to Modification 1; Fig. 6 is a cross-sectional view showing the configuration of battery cushioning materials arranged between battery cells according to Modification 2; and Fig. 7 is a schematic view showing the arrangement position of battery cushioning materials according to Modification 5 in the XY plane.

[0008] An embodiment of the present invention will be described below. FIG. 1 is a schematic cross-sectional view showing a secondary battery 1 according to this embodiment. As shown in FIG. 1, the secondary battery 1 includes a plurality of battery cells 2 and battery cushioning materials 10 arranged between the battery cells 2. The secondary battery 1 also includes a package 3 that encloses the battery cells 2, and current collectors 4 connected to the battery cells 2 extend from the package 3. Here, the stacking direction of the plurality of battery cells 2 corresponds to the first direction in the present disclosure and will be referred to as the Z direction hereinafter. Furthermore, a direction perpendicular to the Z direction is defined as the X direction, and a direction perpendicular to the X and Z directions is defined as the Y direction.

[0009] FIG. 2 is an enlarged cross-sectional view showing a portion of a battery cell 2. Each battery cell 2 has a known configuration, for example, a stack of a positive electrode current collector 21, a positive electrode layer 22, a solid electrolyte layer 23, and a negative electrode current collector 24. The positive electrode current collector 21 and the negative electrode current collector 24 are made of a metal material such as aluminum, nickel, iron, stainless steel, titanium, or copper, and are formed in the shape of a rectangular thin plate. The positive electrode current collector 21 has a positive electrode lead electrode 211 (see FIG. 1) extending from one side forming the outer edge and connected to one of the current collectors 4. Similarly, the negative electrode current collector 24 has a negative electrode lead electrode 241 (see FIG. 1) extending from one side forming the outer edge and connected to the other current collector 4.

[0010] The positive electrode layer 22 is provided between the positive electrode current collector 21 and the solid electrolyte layer 23. The positive electrode layer 22 is made of a positive electrode active material. Examples of the positive electrode active material include LiMn ２ O ４ , LiCoO ２ , LiNiO ２, Li(Ni-Mn-Co)O ２ Examples of the lithium-transition metal oxides include those in which a part of the transition metal is replaced by another element, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds.

[0011] The solid electrolyte layer 23 contains a solid electrolyte as a main component and is a layer interposed between the positive electrode layer 22 and the negative electrode current collector 24. Examples of the solid electrolyte material include sulfide solid electrolytes and oxide solid electrolytes, but sulfide solid electrolytes are preferred. Examples of sulfide solid electrolytes include LPS-based (e.g., argyrodite (Li ６ P.S. ５ Cl), LGPS system (e.g. Li １０ GeP ２ S １２ 2 shows an example in which the positive electrode layer 22, the solid electrolyte layer 23, and the negative electrode current collector 24 are laminated only on one surface of the positive electrode current collector 21, but a configuration in which the positive electrode layer 22, the solid electrolyte layer 23, and the negative electrode current collector 24 are laminated on both surfaces of the positive electrode current collector 21 may also be used.

[0012] The secondary battery 1 of this embodiment is an all-solid-state battery having a solid electrolyte layer 23 as described above. Such all-solid-state batteries expand and contract during charging and discharging, and the difference in displacement (stroke length) between expansion and contraction is greater than that of lithium-ion batteries that use liquid electrolytes. Therefore, it is necessary to dispose battery cushioning materials 10 between each battery cell 2, which can absorb the displacement during contraction of the battery cells 2 from the displacement during expansion of the battery cells 2 and can apply a uniform pressing force to each battery cell 2 to prevent a decrease in battery performance.

[0013] 3 is a cross-sectional view showing the configuration of the battery cushioning material 10 arranged between the battery cells 2. FIG. 4 is a schematic diagram showing the arrangement position of the battery cushioning material 10 on the XY plane. Note that FIG. 4 is a cross-sectional view showing the arrangement position of the battery cushioning material 10 on the XY plane. Ｃ4 is a cross-sectional view of a portion of the battery cushioning material 10 taken along the line 10a and 10b, looking toward the second battery cell 2B. In this embodiment, as described above, the battery cushioning material 10 is disposed between each of the plurality of battery cells 2. The battery cushioning material 10 is composed of a plurality of displacement absorbers 11 made of an elastic material. A plurality of displacement absorbers 11 are provided in an XY plane perpendicular to the Z direction. For example, as shown in FIG. 4 , a plurality of displacement absorbers 11 are arranged in an array in the X and Y directions. The specific material of these displacement absorbers 11 is not particularly limited, and examples thereof include silicone rubber and aerogel, and can be selected depending on the displacement difference (stroke length) during charging and discharging of the battery cells 2.

[0014] As shown in FIG. 3 , each displacement absorber 11 constituting the battery cushioning material 10 includes a cell contact surface 12 that contacts the battery cell 2 and a displacement absorbing portion 13 that protrudes from the cell contact surface 12 in the direction away from the battery cell 2 (Z direction). The displacement absorbing portion 13 is configured so that the cross-sectional area of ​​the cross section perpendicular to the Z direction (the XY plane, i.e., the plane parallel to the cell contact surface 12) decreases with increasing distance from the cell contact surface 12. Specifically, if one of two adjacent battery cells 2 (the -Z side) is a first battery cell 2A and the other (the +Z side) is a second battery cell 2B, the displacement absorbing portion 13 is composed of a first absorption portion 13A joined to the first battery cell 2A via the cell contact surface 12A and a second absorption portion 13B joined to the second battery cell 2B via the cell contact surface 12B. In other words, the displacement absorbing portion 13 is composed of multiple absorption portions aligned in the Z direction.

[0015] In this embodiment, the first absorption section 13A and the second absorption section 13B are formed in a trapezoidal shape when viewed in a cross section taken along the XZ plane as shown in FIG. 3 . Although not shown, the first absorption section 13A and the second absorption section 13B are also formed in a trapezoidal shape when viewed in a cross section taken along the YZ plane. That is, the cross-sectional area of ​​the first absorption section 13A in a plane parallel to the XY plane gradually decreases with increasing distance from the cell contact surface 12A, and the cross-sectional area of ​​the second absorption section 13B in a plane parallel to the XY plane gradually decreases with increasing distance from the cell contact surface 12B. When the first absorption section 13A and the second absorption section 13B are pressed in the Z direction, the first absorption section 13A and the second absorption section 13B elastically deform in the XY directions along which there is a gap. This allows the stroke length during expansion and contraction of the battery cell 2 to be absorbed, suppressing displacement in the Z direction. The reaction force from the pressing force received from the battery cell 2 allows each displacement absorber 11 to press the battery cell 2 with uniform surface pressure.

[0016] Here, the ends 121A, 121B of the cell contact surfaces 12A, 12B are the starting points of the displacement absorbing sections 13 whose cross-sectional area changes as they move in the Z direction, and correspond to the area change starting points of the present disclosure. In this embodiment, the multiple displacement absorbers 11 are continuous at the ends 121A, 121B of the cell contact surfaces 12, which are the area change starting points. That is, as shown in FIG. 3 , adjacent first absorbent sections 13A are continuous in the X direction at the ends 121A (area change starting points) of the cell contact surfaces 12A. Similarly, the second absorbent sections 13B are continuous in the X direction at the ends 121B (area change starting points) of the cell contact surfaces 12B. Although not shown, the same applies to the Y direction. The fact that the displacement absorbers 11 arranged in an array along the X and Y directions are continuous at the ends 121A, 121B of the cell contact surfaces 12A, 12B means that when the displacement absorbers 11 are viewed from the Z direction as shown in Fig. 4, adjacent displacement absorbers 11 in the X and Y directions are continuous without gaps at the outer peripheries of the first absorber section 13A and the second absorber section 13B (only the outer periphery of the second absorber section 13B is shown in Fig. 4). As a result, there is no flat area between adjacent displacement absorbers 11 where surface pressure can escape.

[0017] In this embodiment, a plane (center plane S) that passes through the midpoint of the distance between two adjacent battery cells 2 and is perpendicular to the Z direction is Ｃ), each displacement absorbing section 13 has an asymmetric shape. For example, in this embodiment, the first absorbent section 13A has a greater length (thickness) along the Z direction than the second absorbent section 13B. Also, the first end face 131A on the +Z side of the first absorbent section 13A has a smaller area than the second end face 131B on the −Z side of the second absorbent section.

[0018] When stress due to expansion or contraction of the battery cell 2 is applied in the Z direction, the displacement amount during elastic deformation varies between the first absorption section 13A and the second absorption section 13B. That is, when a force F is applied to an absorption section (first absorption section 13A or second absorption section 13B) and it is displaced by an amount x, Hooke's law establishes F = kx, where k is the spring constant of the absorption section. In other words, x = F / k, and the smaller the spring constant k, the larger the displacement amount x. This means that to achieve a desired stroke length for the difference in displacement between expansion and contraction of the battery cell 2, the spring constant k can be adjusted according to the desired stroke length.

[0019] Furthermore, the elastic modulus E (longitudinal modulus, Young's modulus) of the absorbing section is calculated by E = σ / ε using the strain ε when stress σ is applied. If the cross-sectional area of ​​the absorbing section in the XY plane at an arbitrary distance from the cell contact surface 12 in the Z direction is A, the stress σ at the position of said cross-sectional area A is σ = F / A. The strain ε is the displacement x relative to the thickness t of the absorbing section, and is expressed by ε = x / t. Therefore, the spring constant k can be expressed by the following equation (1).

[0020]

[0021] Formula (1) means that the spring constant k can be controlled by the thickness t of the absorbent section in the Z direction and the cross-sectional area A. Therefore, in this embodiment, the thickness t of each of the first absorbent section 13A and the second absorbent section 13B, the cross-sectional area A at the distance from the cell contact surfaces 12A, 12B (the shape of the first absorbent section 13A and the second absorbent section 13B), and the elastic modulus E of each of the first absorbent section 13A and the second absorbent section 13B are set according to the desired stroke length to be ensured.

[0022] Furthermore, in this embodiment, the first end face 131A of the first absorption section 13A facing the second battery cell 2B and the second end face 131B of the second absorption section 13B facing the first battery cell 2A have different areas, and the first end face 131A has a smaller area than the second end face 131B. That is, the entire surface of the first end face 131A contacts the second end face 131B, and a portion of the second end face 131B contacts the first end face 131A. As a result, even if misalignment occurs between the first absorption section 13A and the second absorption section 13B when aligning the first absorption section 13A and the second absorption section 13B, the contact area between the first end face 131A and the second end face 131B does not change, and a displacement absorption section 13 with desired performance can be obtained.

[0023] Furthermore, in this embodiment, the second absorbent section 13B, which has a smaller thickness t, has a higher elastic modulus than the first absorbent section 13A, which has a larger thickness t. That is, the distance from the cell contact surface 12B of the second absorbent section 13B to the second end surface 131B is shorter than the distance from the cell contact surface 12A of the first absorbent section 13A to the first end surface 131A. This increases the load transferability when the load from the first absorbent section 13A is transferred from the second absorbent section 13B to the cell contact surface 12B, and also increases the load transferability when the load from the second battery cell 2B is transferred from the second absorbent section 13B to the first absorbent section 13A. By making the second absorbent section 13B have a higher elastic modulus than the first absorbent section 13A, the load is less likely to be dispersed in the second absorbent section 13B, allowing for uniform pressure to be applied to the cell contact surface 12B.

[0024] A specific configuration for making the elastic modulus of the second absorbent section 13B greater than that of the first absorbent section 13A is, for example, to use a material for the second absorbent section 13B having a greater elastic modulus than the material for the first absorbent section 13A. In this case, the elastic moduli of the first absorbent section 13A and the second absorbent section 13B will be values ​​that correspond to the quality of the constituent materials. Therefore, in order to set the elastic modulus values ​​more precisely, it is preferable to form the displacement absorbing section 13 from a foam or to use a filler-containing material. Below, we will explain the cases where a foam and a filler-containing material are used for the displacement absorbing section 13.

[0025] When the displacement absorbing portion 13 is made of a foam, the Young's modulus (longitudinal elastic modulus) E＊ is the Young's modulus (longitudinal elastic modulus) E of the constituent material Ｓ , density of foam ρ ＊ , density of constituent material ρ Ｓ , constant C １ Using the above, it is expressed by the following equation (2).

[0026]

[0027] Therefore, the density ρ of the foam in the first absorbent section 13A and the second absorbent section 13B ＊ For example, when the first absorbent section 13A and the second absorbent section 13B are made of the same material, the density ρ of the foam of the second absorbent section 13B is ＊ is the density ρ of the foam of the first absorbent section 13A. ＊ In other words, the porosity of the first absorbent section 13A may be made larger than the porosity of the second absorbent section 13B. In this case, it is preferable to use a foam formed by open cell foam for the first absorbent section 13A and a foam formed by closed cell foam for the second absorbent section 13B. This makes it possible to make the porosity of the first absorbent section 13A larger than the porosity of the second absorbent section 13B, and to make the modulus of elasticity of the second absorbent section 13B larger than the modulus of elasticity of the first absorbent section 13A.

[0028] In addition, when the displacement absorbing portion 13 is made of a filler-containing material, the Young's modulus (longitudinal elastic modulus) E of the filler-containing material is ｆ , Young's modulus E of the constituent material ｍ , the filler aspect ratio c, and the filler content Vf are expressed by the following formula (3): The filler aspect ratio c is expressed as c=λ / 2d, where λ is the filler length and d is the filler diameter.

[0029]

[0030] In addition, in equation (3), η １ satisfies the condition of the following formula (4) using a filler orientation index α (a random tentative value of 16).

[0031]

[0032] Therefore, the filler content V ｆ By changing η, it is possible to make the elastic modulus of the first absorbent section 13A and the second absorbent section 13B different. In other words, by making the filler content of the first absorbent section 13A smaller than the filler content of the second absorbent section 13B, the elastic modulus of the second absorbent section 13B becomes larger than the elastic modulus of the first absorbent section 13A. Furthermore, from equations (3) and (4), η １ In other words, the elastic modulus (Young's modulus) E of the filler is increased. ｆ Therefore, by making the elastic modulus of the filler contained in the second absorbent section 13B greater than the elastic modulus of the filler contained in the first absorbent section 13A, the elastic modulus of the second absorbent section 13B becomes greater than the elastic modulus of the first absorbent section 13A.

[0033] As described above, by using foam or filler-containing materials for the first absorbent section 13A and the second absorbent section 13B in addition to the constituent materials thereof, the elastic modulus E of the first absorbent section 13A and the second absorbent section 13B can be set to a desired value. Furthermore, by selecting the shapes and elastic moduli of the first absorbent section 13A and the second absorbent section 13B, it is possible to set the spring constant k shown in equation (1) more precisely, and a displacement absorbing section 13 corresponding to a desired stroke length can be obtained.

[0034] [Effects of the Present Embodiment] The battery cushioning material 10 of the present embodiment is disposed between multiple battery cells 2 and includes multiple displacement absorbers 11. These displacement absorbers 11 have cell contact surfaces 12 that contact the battery cells 2 and displacement absorbing portions 13 that extend from the cell contact surfaces 12 in the Z direction and whose cross-sectional area in a plane parallel to the XY plane decreases with increasing distance from the cell contact surfaces 12. When the ends 121A, 121B of the cell contact surfaces 12 are taken as the starting points of area change, adjacent displacement absorbers 11 are continuous at the starting points of area change. Therefore, the battery cushioning material 10 of the present embodiment does not have flat portions between adjacent displacement absorbers 11, preventing surface pressure loss. This allows the reaction force of the force absorbed by the displacement absorbers 11 to be uniformly transmitted from the cell contact surfaces 12A, 12B to the battery cells 2, allowing the battery cells 2 to be pressed with uniform force, thereby suppressing deterioration of battery performance.

[0035] In this embodiment, the displacement absorbing portion 13 is formed on a plane perpendicular to the Z direction (a central plane S Ｃ ) and the center plane S Ｃ The amount of displacement differs between the first battery cell 2A side and the second battery cell 2B side. In other words, by selecting the shape of the displacement absorbing section 13, it is possible to set the shape of the displacement absorbing section 13 corresponding to the desired stroke length, which applies appropriate pressure to each battery cell 2 and also makes it possible to keep the amount of volume change due to expansion and contraction of the secondary battery 1 within a desired range.

[0036] The displacement absorbing section 13 is composed of a first absorption section 13A and a second absorption section 13B aligned in the Z direction. The first absorption section 13A and the second absorption section 13B have different areas of the opposing first end faces 131A and second end faces 131B. If the first end face 131A and the second end face 131B were the same area, the entire surface of the first end face 131A and the entire surface of the second end face 131B would need to be in contact. Even if slight misalignment occurs when aligning the first absorption section 13A and the second absorption section 13B, the contact area would fluctuate. In this case, the amount of elastic deformation of the displacement absorbing section 13 would change, and the displacement difference due to the expansion and contraction of the battery cell 2 may not be fully absorbed. In contrast, by making the areas of the first end face 131A and the second end face 131B different as described above, the tolerance for misalignment can be increased. Even if misalignment occurs, there will be no difference in the amount of elastic deformation as long as it is within the tolerance. This makes it possible to obtain a displacement absorbing section 13 that corresponds to the desired stroke length when the battery cell 2 expands or contracts.

[0037] In this embodiment, the first absorption section 13A and the second absorption section 13B have different thicknesses t in the Z direction. When stress due to expansion or contraction of the battery cell 2 is applied in the Z direction, the amount of displacement during elastic deformation varies between the first absorption section 13A and the second absorption section 13B. Therefore, by appropriately selecting the thicknesses of the first absorption section 13A and the second absorption section 13B, it is possible to adjust the stroke length, and the shape of the displacement absorption section 13 can be set to obtain the desired stroke length.

[0038] In this embodiment, the first absorbent section 13A is thicker in the Z direction than the second absorbent section 13B, and the thinner second absorbent section 13B has a higher elastic modulus than the first absorbent section 13A. The thinner second absorbent section 13B increases the load transferability, i.e., the load from the first absorbent section 13A is transferred from the second absorbent section 13B to the cell contact surface 12B, and the load from the second battery cell 2B is transferred from the second absorbent section 13B to the first absorbent section 13A. By making the elastic modulus of the second absorbent section 13B greater than the elastic modulus of the first absorbent section 13A, the load is less likely to be dispersed, and uniform pressure can be applied to the cell contact surface 12B.

[0039] In this embodiment, the displacement absorbing section 13 may be made of a foam (porous body). In this case, the first absorbent section 13A, which has a larger thickness in the Z direction, has a foam porosity greater than that of the second absorbent section 13B. In other words, the density ρ of the foam of the first absorbent section 13A is ＊ is the density ρ of the foam of the second absorbent section 13B ＊ This allows the modulus of elasticity of the second absorbent section 13B to be greater than the modulus of elasticity of the first absorbent section 13A, as described above.

[0040] In this case, it is preferable that the second absorbent section 13B is a foam formed by closed cell foaming, and the first absorbent section 13A is a foam formed by open cell foaming, which makes it easy to obtain a displacement absorbing section 13 in which the elastic modulus of the second absorbent section 13B is greater than the elastic modulus of the first absorbent section 13A.

[0041] In this embodiment, the displacement absorbing section 13 may be a filler-containing body. In this case, the first absorbent section 13A, which has a larger thickness, has a higher filler content than the second absorbent section 13B. This makes it possible to easily obtain a displacement absorbing section 13 in which the modulus of elasticity of the second absorbent section 13B is greater than the modulus of elasticity of the first absorbent section 13A, simply by controlling the filler content.

[0042] Furthermore, the filler contained in the first absorbent section 13A may have a smaller elastic modulus than the filler contained in the second absorbent section 13B. In this way, by selecting the filler contained in the first absorbent section 13A or the second absorbent section 13B, it is possible to easily obtain a displacement absorbing section 13 in which the elastic modulus of the second absorbent section 13B is greater than the elastic modulus of the first absorbent section 13A.

[0043] [Modifications] The present invention is not limited to the above-described embodiment, and includes the following modifications within the scope of achieving the object of the present invention.

[0044] [Modification 1] In the above embodiment, the displacement absorbing portion 13 is Ｃ As an example of an asymmetrical configuration with respect to the battery cell contact surface 12, as shown in Fig. 3, the first absorbent section 13A and the second absorbent section 13B are each trapezoidal in cross section, and the areas of the first end surface 131A and the second end surface 131B and the thickness t in the Z direction are different from each other. However, this is not limiting. Fig. 5 is a cross-sectional view showing the configuration of a battery cushioning material 10 arranged between battery cells 2 according to Modification 1. For example, as shown in Fig. 5, either or both of the first absorbent section 13A and the second absorbent section 13B may be formed in a semicircular or semielliptical shape in cross section. Even in this case, the spring constant k shown in equation (1) changes depending on the distance from the cell contact surface 12, and the amount of elastic deformation of the first absorbent section 13A and the second absorbent section 13B can be made different.

[0045] In the example shown in FIG. 5, the first end surface 131A of the first absorbent section 13A and the second end surface 131B of the second absorbent section 13B are aligned with the center plane S Ｃ As in the first embodiment, the contact occurs at the center plane S Ｃ The contact may be made on the second battery cell 2B side or on the first battery cell 2A side.

[0046] [Modification 2] In the above embodiment, the displacement absorbing portion 13 is Ｃ Although an example of a configuration in which the shape is asymmetric with respect to the center plane S is shown, a symmetric shape may also be used. Fig. 6 is a cross-sectional view showing the configuration of a battery cushioning material 10 arranged between battery cells 2 according to Modification 2. For example, as shown in Fig. 6, the first absorption section 13A and the second absorption section 13B have the same shape, and the center plane SＣ Even in this case, the first absorbent section 13A and the second absorbent section 13B may be made of a foam with different porosities, or may be made of a filler-containing material with different filler contents or elastic moduli, thereby making the spring constants k of the first absorbent section 13A and the second absorbent section 13B different and allowing them to have different amounts of elastic deformation.

[0047] [Variant 3] In the above embodiment, a displacement absorption section 13 having two absorption sections (first absorption section 13A, second absorption section 13B) arranged in the Z direction is exemplified, but a displacement absorption section 13 having three or more absorption sections arranged may also be used.

[0048] [Modification 4] In the above embodiment, the shape of each displacement absorber 11 is rectangular as viewed from the Z direction as shown in Fig. 4, but this is not limiting. Each displacement absorber 11 may be formed in a polygonal shape, and adjacent displacement absorbers 11 may be adjacent to each other along each side of the polygon.

[0049] [Variation 5] In the above embodiment, as shown in FIG. 4 , multiple displacement absorbers 11 are arranged in an array in the X and Y directions. However, multiple displacement absorbers elongated in the X direction may be arranged in the Y direction, or multiple displacement absorbers elongated in the Y direction may be arranged in the X direction. FIG. 7 is a schematic diagram showing the arrangement position of a battery cushioning material 10 according to Variation 5 in the XY plane and its cross-sectional shape when cut in the YZ plane. Note that in FIG. 7 , the first absorption section 13A is not shown, and only the contact position of the first end surface 131A of the first absorption section 13A that contacts the second absorption section 13B is indicated by a dashed line. In the example shown in FIG. 7 , multiple second absorption sections 13B elongated in the X direction are arranged side by side in the Y direction. Note that, although not shown, the same applies to the first absorption sections 13A constituting the displacement absorber 11, where multiple first absorption sections 13A elongated in the X direction are arranged side by side in the Y direction. As in the above embodiment, the first end surface 131A of the first absorbent section 13A contacts the second end surface 131B of the second absorbent section 13B. The second absorbent section 13B configured in this manner is formed, for example, by pressing a plurality of processing rollers rotating about the Y axis against a plate-shaped elastic material, and rotating the processing rollers to move the elastic material in the X direction. This makes it possible to easily form a plurality of second absorbent sections 13B elongated in the X direction, as shown in FIG. 7, thereby reducing manufacturing costs. The first absorbent section 13A can also be formed using a similar method.

[0050] [Variation 6] In the above embodiment, an example was shown in which the first absorbent section 13A is made of a foam formed by open cell foam and the second absorbent section 13B is made of a foam formed by closed cell foam, as a configuration in which the second absorbent section 13B has a higher elastic modulus than the first absorbent section 13A. In contrast, the displacement absorbing section 13 may be made of a foam whose porosity decreases from the first absorbent section 13A toward the second absorbent section 13B. The same applies when a filler-containing material is used; the filler content may increase from the first absorbent section 13A toward the second absorbent section 13B, or a configuration in which a filler with a greater elastic modulus is contained from the first absorbent section 13A toward the second absorbent section 13B may be used.

[0051] 1... Secondary battery, 2... Battery cell, 2A... First battery cell, 2B... Second battery cell, 10... Battery cushioning material, 11... Displacement absorbing body, 12, 12A, 12B... Cell contact surface, 13... Displacement absorbing portion, 13A... First absorbing portion, 13B... Second absorbing portion, 121A, 121B... End portion (area change point), 131A... First end surface, 131B... Second end surface, S Ｃ ...Central plane.

Claims

1. A battery cushioning material arranged between a plurality of battery cells, comprising a plurality of displacement absorbers each having a cell contact surface that contacts the battery cell and a displacement absorbing portion that extends in a first direction away from the cell contact surface and whose cross-sectional area in a cross section perpendicular to the first direction decreases with increasing distance from the cell contact surface, wherein adjacent displacement absorbers are continuous at the area change starting point, which is the end of the cell contact surface when cross-sectioned in a plane perpendicular to the cell contact surface.

2. The battery cushioning material according to claim 1, wherein the displacement absorbing portion has an asymmetric shape with respect to a central plane that passes through a point that bisects the distance between the opposing battery cells and is parallel to the cell contact surface.

3. The battery cushioning material according to claim 2, wherein the displacement absorbing section is composed of a plurality of absorbing sections arranged in the first direction, and the opposing end faces of each absorbing section have different areas.

4. The battery cushioning material according to claim 2, wherein the displacement absorbing section is composed of a plurality of absorbing sections aligned in the first direction, and the thicknesses of the absorbing sections along the first direction are different from one another.

5. The battery cushioning material according to claim 4, wherein the absorbing section having a smaller thickness in the first direction has a higher elastic modulus than the absorbing section having a larger thickness in the first direction.

6. The battery cushioning material according to claim 5, wherein the displacement absorbing section is made of a porous body, and the absorbing section having a larger thickness in the first direction has a larger porosity of the porous body than the absorbing section having a smaller thickness in the first direction.

7. The battery cushioning material according to claim 5, wherein the displacement absorbing section is made of a porous material, the absorbing section having a small thickness in the first direction is made of closed-cell foam, and the absorbing section having a large thickness in the first direction is made of open-cell foam.

8. The battery cushioning material according to claim 5, wherein the displacement absorbing portion is a filler-containing body, and the absorbing portion having a larger thickness in the first direction has a smaller filler content than the absorbing portion having a smaller thickness in the first direction.

9. The battery cushioning material according to claim 5, wherein the displacement absorbing section is a filler-containing body, and the filler contained in the absorbing section having a larger thickness in the first direction has a smaller elastic modulus than the filler in the absorbing section having a smaller thickness in the first direction.

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